The present invention relates to an expansion tank with plural expansion chambers.
The amount of air which can be supplied to a supercharged combustion engine depends on the pressure of the air but also on the temperature of the air. Supplying as large an amount of air to the combustion engine as possible entails effective cooling of the air before it is led to the combustion engine. Effective cooling of the charge air may be achieved by subjecting it to two steps of cooling. The charge air may be subjected to a first step of cooling in a first charge air cooler by coolant from the combustion engine's cooling system. This first step may cool the charge air to a temperature close to the temperature of the coolant. The charge air may thereafter be subjected to a second step of cooling in a second charge air cooler by coolant from a low-temperature cooling system. The charge air may thus be cooled to a temperature close to the temperature of the surroundings.
The technique known as EGR (exhaust gas recirculation) is a known way of recirculating part of the exhaust gases from a combustion process in a combustion engine. The recirculating exhaust gases are mixed with the charge air before it is led to the cylinders of the combustion engine. Adding exhaust gases to the air causes a lower combustion temperature resulting inter alia in a reduced content of nitrogen oxides NOx in the exhaust gases. This technique is used both for Otto engines and for diesel engines. Supplying a large amount of exhaust gases to the combustion engine entails here again effective cooling of the exhaust gases before they are led to the combustion engine. The exhaust gases may likewise be cooled in two stages. They may be subjected to a first step of cooling in a first EGR cooler by coolant from the combustion engine's cooling system and a second step of cooling in a second EGR cooler by coolant from the low-temperature cooling system. Thus the exhaust gases too may be cooled to a temperature close to the temperature of the surroundings.
Cooling of charge air and recirculating exhaust gases in two stages as above entails using two separate cooling systems. The coolants in the respective cooling systems are of the same kind but have different working temperatures during operation. It is therefore not appropriate for the coolants to be mixed. The coolants become warmer during operation in the respective cooling systems, which means that they assume a larger volume. To cater for coolant volume change, each cooling system has its own expansion tank. On the occasion of servicing, the coolant levels in the respective expansion tanks in the cooling systems are checked and replenished as necessary.